Parental help ‘allows fish and birds to lay smaller eggs’

BIRDS and fish within social groups that can support parental duties may have evolved the ability to produce smaller eggs to conserve energy, research suggests.

A Cambridge University study found that females in some cooperatively breeding species reduce the size of their eggs when other group members are available to help protect, incubate and feed offspring after laying.

The study, published in the scientific journal Peerj, suggests that this extra help means females do not need to provide as much food to offspring at the nest and may save energy. This allows them to increase their own chances of survival to the next year or to have their next set of offspring sooner.

Researchers looked at data from 12 studies on 10 species of cooperatively breeding vertebrates to analyse the relationship between the number of helpers present and egg size.

They found females in bird species such as the sociable weaver and superb fairy-wren, along with daffodil cichlid fish, tend to produce smaller eggs when help with rearing is at hand compared to when parents are alone.

This was most marked in species where mothers also reduce energy put into post-natal care as other members of the social group are helping them.

Tanmay Dixit, lead author of the paper, who carried out the study for his third-year dissertation while studying for an undergraduate degree in Natural Sciences at St John’s College, Cambridge, said: “While this paper does not provide conclusive evidence as it is based on a small sample of studies and species, it suggests that it is at least possible that the females of certain cooperatively breeding species may be able to adapt their reproductive decisions to changes in the social environment by reducing investment in current broods to prioritise future survival and reproduction.”

He said further research was needed to confirm whether individual females were able to alter the size of offspring.